Alex Mercer, also known as Zeus, is actually Blacklight, a liquid virus engineered by the real Alex Mercer, who's fellows were being murdered. After Dr. Mercer was cornered at Penn Station, he threw the vial to the ground, before being shot by soldiers of Blackwatch, a paramilitary group created to destroy viruses. The virus then took over his body, and Alex Mercer awoke with no memories in a morgue. He has a sister, Dr. Mercer's sister, Dana. He also has the ability to shapeshift into anything.